The present invention relates to a sliding member and more particularly to a sliding member having heat resistance. The present invention relates also to a method for manufacturing the same.
At this point, it is to be noted that throughout the Specification and claims the term "sliding member having heat resistance" is used to designate a product that is capable of carrying a load with a relatively low coefficient of friction even under conditions in which the application of normally utilized lubricants is difficult due to high temperatures and at the same time exhibits a sealing function, e.g. bearing bushes, washers, sliding plates, contact type packings, etc.
Hitherto, as sliding members of this kind those that have been publicly known have metallic materials made of stainless steel or copper alloy within which are embedded solid lubricant pellets, or nonmetallic materials such as graphite, or ceramics, etc., or compound materials such as the so-called cermet, etc., or heat resistant plastic material such as polytetrafluoroethylene (PTFE), polyimide, etc.
However, although all of those known materials are superior in heat resistance they have problems in friction and wear under dry friction conditions, and difficulties in mechanical strength, in particular resistance to impact, not necessarily having good conformability with mating members, and also problems in that they cannot exhibit their function sufficiently in regard to minute slippages.
In order to resolve those problems or difficulties, e.g. as disclosed in U.S. Pat. No. 3,404,061 or Japanese Patent Publication No. 23,966/1969, a technique to manufacture a sliding member has been developed in which the sliding member is manufactured by shaping expanded graphite, which is obtainable by a special treatment of graphite, together with reinforcing materials. Although this sliding member reveals superior heat resistance and its impact strength is remarkably improved compared with conventional sliding members, the coefficient of friction is somewhat higher than that of conventional sliding members and it also has a defect in that it often makes abnormal frictional noises under dry friction conditions.
Further, sliding members which are obtained by shaping mica or asbestos together with reinforcing materials also have been publicly known, but they have similar problems and difficulties.
This is thought to reside in the fact that in these members the difference between the coefficient of static and dynamic friction is large, and that they possess somewhat soft characteristics, etc. It is also conceivable that the shapes of the respective parts constituting the sliding system and the natural vibrations of the materials influence these problems.
Some of the present inventors have already proposed a sliding member in order to resolve the problems as above described in Japanese patent application No. 120,701/1981 which member has a lubricating property appropriate for use over a wide temperature range from room to high temperatures and which is characterized in that the surface of a basic sliding member which is obtainable by shaping heat resistant material together with metal meshes comprised of woven or knitted metal filaments as reinforcing material, is covered with lubricating compounds, and they confirmed that it, generally fulfils the expected objectives.